Exhaust gas dry treatment devices having an adsorption tower filled with a granular adsorbent are in use in order to remove the sulfur oxides, nitrogen oxides, etc. contained in an exhaust gas such as boiler exhaust gas, sintering furnace exhaust gas or the like. The adsorbent includes, for example, a carbonaceous adsorbent, an alumina-based adsorbent and a silica-based adsorbent. The carbonaceous adsorbent is capable of treating an exhaust gas at relatively low temperatures and removing various harmful substances simultaneously; therefore, it is superior to other adsorbents.
The carbonaceous adsorbent includes, for example, activated carbon and activated coke, and a pelletized adsorbent of about 0.5 to 4 cm is preferred particularly. These are known adsorbents. Patent Literature 1 shows the outline of an exhaust gas treatment device using a carbonaceous adsorbent.
This exhaust gas treatment device has, as shown in FIG. 25, an adsorption tower 10, a regeneration tower 90, a sieve 91, an adsorbent storage tank 92, a by-product recovery apparatus 93, etc. Inside the adsorption tower 10 are formed moving beds filled with a granular adsorbent. An exhaust gas of 100 to 200° C. is contacted with the adsorbent in the moving beds, whereby the harmful components contained in the exhaust gas can be removed.
Ammonia, urea, etc. are added into an exhaust gas; the mixture is sent to the adsorption tower; thereby, the nitrogen oxides in the exhaust gas are decomposed into nitrogen and water by the catalytic action of the adsorbent. Other harmful components are removed mainly by the adsorptivity of the adsorbent.
The regeneration tower 90 is an apparatus for regeneration of adsorbent. The adsorbent adsorbs harmful components in the treatment of exhaust gas; dust, etc. adhere onto the surfaces of the adsorbent; the adsorptivity of the adsorbent is reduced gradually. The adsorbent reduced in the adsorptivity is withdrawn from the adsorption tower 10 and carried to the regeneration tower 90 by a conveyor line 94. Inside the regeneration tower 90, the adsorbent is heated to a high temperature in a nearly oxygen-free atmosphere. Thereby, the harmful components are desorbed and the adsorbent is regenerated. The regenerated adsorbent is cooled and returned back to the adsorption tower 10 by a conveyor line 95.
The sieve 91 is for removal of fine powder from adsorbent. The fine powder includes, for example, the dust removed from the exhaust gas in the adsorption tower 10 and the adsorbent which was powdered by abrasion during the circulation between the adsorption tower 10 and the regeneration tower 90. The fine powder removed by the sieve 91 is stored in a hopper 96 and discharged outside the system.
The adsorbent storage tank 92 is a storage tank of fresh adsorbent. The adsorbent is partially powdered and discharged outside the system and is partially consumed by the reaction; therefore, a fresh portion of adsorbent need be supplied incessantly. The exhaust gas containing harmful components is introduced into the adsorption tower 10 via an exhaust gas supply duct 98. The treated exhaust gas is sent to a chimney 97 via an exhaust gas discharge duct 99 and then discharged into the air. The harmful components composed mainly of sulfur oxides, discharged from the regeneration tower 10 are treated in the by-product recovery apparatus 93, and sulfuric acid, for example, is produced.
The Patent Literature 1 gives a detailed description on the adsorption tower 10. Citing the description, the adsorption tower 10 is explained referring to FIGS. 20 to 24. The adsorption tower 10 has a boxed-shaped tower body 20, two exhaust gas supply ports 25a and 25b formed in the front tower wall 21 of the tower body 20, and three exhaust gas discharge ports 26a, 26b and 26c formed in the rear tower wall 22 facing the front tower wall 21 (FIGS. 20 and 22).
Inside the tower body 20 are provided a plurality of reaction chambers 51, 52, 53 and 54 which form moving beds therein (FIGS. 21 and 22). The reaction chambers 51 to 54 are each provided vertically and nearly parallel from the front tower wall 21 toward the rear tower wall 22 facing the front tower wall 21 and from the tower top wall 27 to the tower bottom wall 28.
The reaction chambers 51 to 54 are each constituted by three units 30, 30 and 30, as shown in FIG. 22. As shown in FIG. 23, each unit 30 is formed in a flat box shape and has a gas-flowing section 38 through which an exhaust gas flows in a horizontal direction (an arrow X direction). Above the gas-flowing section 38 is formed an adsorbent supply section 37, and an adsorbent discharge section 39 is formed below the gas-flowing section 38. The gas-flowing section 38 has four sides; opposing two wide sides are formed as a gas-incoming surface 31 and a gas-leaving surface 32; and other two narrow sides 33 and 34 are closed.
In the unit 30, the supply section 37 has at least one supply port 35 (2 ports in the Fig.) and the discharge section 39 has at least one discharge port 36 (2 ports in the Fig.). An adsorbent is continuously fed from the supply port 35 and is discharged continuously from the discharge port 36, whereby a moving bed of adsorbent is formed in the unit. In the moving bed, the adsorbent at the gas-incoming surface 31 side adsorbs harmful substances in a larger amount than the adsorbent at the gas-leaving surface 32 side. As a result, the adsorptivity of the adsorbent falls sharply. Hence, the flowing-down speed of adsorbent at the gas-incoming surface 31 side is made higher than that at the gas-leaving surface 32 side, in many cases.
The gas-incoming surface 31 and the gas-leaving surface 32 are formed by a louver, a perforated plate, or the like. Owing to such a structure, the adsorbent flowing down in the unit 30 can be kept in the unit 30 and the passage of exhaust gas through unit 30 is made possible. In one case, the area of gas-incoming surface 31 (gas-leaving surface 32) in one unit 30 is about 100 m2. One unit 30 can treat an exhaust gas by about several tens of thousands Nm3/h.
The reaction chambers 51 to 54 each comprise three connected units 30. A gas-incoming surface 31 and a gas-leaving surface 32 are formed at the two sides of three units, facing each other in a direction intersecting at right angles with the connecting direction of three units 30. Each interface between two adjacent units 30 and each interface between the end unit 30 and the tower inner wall are completely closed for prevention of exhaust gas passage.
The reaction chambers 51 and 52 are arranged in such a way that the respective gas-incoming surfaces 31 face each other, and the space q between the two reaction chambers form a gas-incoming passage communicating with an exhaust gas supply port 25a. The reaction chambers 53 and 54 are arranged in such a way that the respective gas-incoming surfaces 31 face each other, and the space r between the two reaction chambers form a gas-incoming passage communicating with an exhaust gas supply port 25b. 
The space s between the reaction chamber 51 and the side tower wall 23 communicates with an exhaust gas discharge port 26a and forms a gas-leaving passage of the exhaust gas which has passed through the reaction chamber 51. The space t between the reaction chamber 52 and the reaction chamber 53 communicates with an exhaust gas discharge port 26b and forms a gas-leaving passage of the exhaust gases which have passed through the reaction chambers 52 and 53. The space u between the reaction chamber 54 and the side tower wall 24 communicates with an exhaust gas discharge port 26c and forms a gas-leaving passage of the gas which has passed the reaction chamber 54.
The adsorption tower 10 has a very wide area for gas flow and can remove the harmful substances contained in an exhaust gas, by the contact of exhaust gas with adsorbent. The adsorbent flows down continuously from each adsorbent supply port 35 toward each adsorbent discharge port 36; a fresh adsorbent is incessantly introduced into the adsorption tower 10; therefore, the adsorption tower 10 can show a constant treatability in its continuous operation.
The adsorption tower 10 has a plurality of exhaust gas supply ports 25a and 25b connected to an exhaust gas supply duct 98. The adsorption tower 10 also has a plurality of exhaust gas discharge ports 26a, 26b and 26c connected to an exhaust gas discharge duct 99. Moreover, the adsorption tower 10 has very large duct sections 45a and 45b of complicated shape between the exhaust gas supply ports 25a and 25b and the front tower wall 21, and has similar duct sections 46a, 46b and 46c between the exhaust gas discharge ports 26a, 26b and 26c and the rear tower wall 22.
These duct sections 45a, 45b, 46a, 46b and 46c need to have each a small sectional shape so as to fit the shape of the duct 98 or 99, at their sides connected to the duct 98 and 99. The duct sections need to have, at their sides connected to the tower body 20, a slender rectangular sectional shape so as to fit the sectional shapes of spaces q and r (gas-incoming passages) and spaces s, t and u (gas-leaving passages). Consequently, the duct sections 45a, 45b, 46a, 46b and 46c have complicated sectional shapes which change sharply, requiring a large ground area.
In FIG. 24 is shown a plan view of arrangement of adsorption tower 10 including an exhaust gas supply duct 98 and an exhaust gas discharge duct 99. As seen in this view, there is a case that the area for arranging the ducts 98 and 99 and duct sections 45a, 45b, 46a, 46b and 46c is larger than the area of tower body 20.
Further, the exhaust gas supply duct 98 and the exhaust gas discharge duct 99 need to be arranged respectively in parallel to the front tower wall 21 and the rear tower wall 22, and no other arrangement is allowed. Since the arrangement of the two ducts 98 and 99 is thus restricted strictly, the arrangement of the adsorption tower 10 undergoes a large restriction.
As described above, the conventional adsorption tower 10 requires duct sections communicating with exhaust gas supply ports and exhaust gas discharge ports and has a complicated and large shape. The adsorption tower 10 needs a large arrangement space and undergoes a large spatial restriction in connection with ducts. As a result, the conventional adsorption tower 10 is complicated in designing, manufacturing and construction, making high the manufacturing cost. Further, in the operation thereof, the inspection, maintenance, cleaning, etc. are complicated, making high the costs thereof.    Patent Literature 1: JP-A-1999-9944